Method for selecting transponders

ABSTRACT

Known methods for the selection of transponders require a large time duration, because in this context the data transmitted according to the half-duplex principle. With the new method, the transponders can be identified with a small time expenditure through the transmission of the time duration of a reference interval, because the data are transmitted in the full-duplex principle.

The present invention relates to a method for the selection oftransponders according to the preamble of the patent claim 1.

Such a method is known from the publication U.S. Pat. No. 5,856,768. Inthis context, the transponders that are located in the HF field of abase station are identified by means of a selection method that operatesin a so-called half-duplex operation. Thereby it is disadvantageous,that much time is required due to the half-duplex method. A furtherdisadvantage of the method exists in that the time duration for thetransmission of the control signals further increases especially if onlya small HF bandwidth is available for the transmission of the controlsignals.

It is the object of the present invention to set forth a method for theselection of transponders, that can be carried out with a small timeexpenditure and that can be realized with few control signals.

This object is achieved according to the invention by a method of theabove initially mentioned type with the characterizing features of thepatent claim 1. Favorable embodiments are the subject of dependentclaims.

Accordingly, the essence of the invention consists in that, in a firststep a base station transmits to the transponders a reference length,which is then used to determine test bits in a following selectionmethod. The selection method operates bit-wise, so that for each bit aselection is made whether a certain group or an individual transponderis selected or whether it shall fall back into a standstill or standbyor silent mode. If a group or an individual transponder is selected, thetransponder or transponders transmits an information signal. The basestation receives these informations and qualitatively acknowledges thesein that it transmits back an information that is then used in thetransponder for the formation of a test bit. If the test bit correspondswith the transmitted information, then the transponder or the group ofthe transponders is further continued to be selected. If the test bitdoes not correspond with the transmitted information, the transponder ortransponders fall back into a standby mode.

For this purpose, the selection of one or more transponders among aplurality of transponders by a base station is carried out by means ofan electromagnetic wave, whereby an information packet (IP) is modulatedonto the electromagnetic wave and the information packet (IP) comprisesa header section (KO) and a data section (DA). Furthermore the datasection (DA) contains a data word with a sequence of bits, whereby onebit is allocated to the bit sequence respectively in a time intervalgenerated from two successive clock pulses. Moreover, an identificationcode embodied as a bit sequence is allocated to each transponder.

Furthermore, the transponders are woken up or activated by the basestation by means of an application or reporting or log-on process,whereby as a result of the log-on process, a pointer in the transponderspoints to a first defined bit of the bit sequence of the identificationcode.

Moreover, in a first step, the time duration of a reference interval istransmitted in the header section of an information packet emitted ortransmitted from the base station. In a second step, the time durationof the reference interval is stored in each transponder, and in a thirdstep at the beginning of the data section each transponder transmits thesignificance or value of the defined bit of the identification code in afirst time interval. In a fourth step, at the end of the first timeinterval, a comparison between time duration of the reference intervaland the time duration of the first time interval is carried out in eachtransponder, and in a fifth step a value is allocated to a test bit fromthe result of the comparison. In a sixth step the transponders comparethe value of the test bit with the value of the first bit transmitted inthe first time interval, and the transponders in which the value of thefirst bit of the bit sequence of the identification code differs fromthe value of the test bit, are switched to a standby mode until thebeginning of a further log-on process. Further, the transponders inwhich the value of the first defined bit of the bit sequence of theidentification code corresponds with the value of the test bit transmitthe value of the following bit of the bit sequence of theiridentification code in a second time interval.

In a further developed embodiment of the method, for the selection offurther or for the selection of exactly one transponder, further or allthe bits of the bit sequence of the identification code are compared, inthat steps 4 to 6 are run through multiple times. In this context, aftereach run-through, the number of the time interval and the number of thebit position of the identification code is increased or reduced by one.

It is an advantage of the method, in comparison to the previous methods,that no reply or response signal needs to be transmitted from the basestation to the transponders after each query or interrogation signal. Ineach run-through, the selection is carried out through the comparison ofthe test bit with one bit of the identification code. Even in a completeselection procedure for the identification of all transponders it issufficient to transmit the reference length for the comparison only oncein one header section of one information packet. The selection of thevalues is determined by the base station through the length of the timeinterval by means of the electromagnetic wave transmitted by it, in thatthe base station reduces or increases the time duration between twosuccessive clock pulses relative to the reference length. In thiscontext, one bit of the identification code of the transponder istransmitted to the base station in connection with each time intervalprescribed by the base station. Thus, the selection method (method foranti-collision) operates in the so-called full-duplex operation.

Hereby the number of the symbols for the control of the selection methodis considerably reduced. Hereby the time for the selection of groups orindividual transponders is considerably reduced. Furthermore, the methodcan be carried out with various different modulation methods, such asfor example, a phase and/or an amplitude modulation.

The inventive methods shall be explained in the following in connectionwith the example embodiments in relation to a schematic drawing. It isshown by

FIG. 1 a an information packet, and

FIG. 1 b a hierarchical arbitration of eight transponders, and

FIG. 2 a a selection of the first of a total of two transponders, and

FIG. 2 b a selection of the second of a total of two transponders.

An information packet IP, consisting of a header section KO, a datasection or region DA and an EOT section or region, is illustrated inFIG. 1 a. Data are transmitted between one or more transponders with abase station by means of such an information packet IP. The number ofthe symbols and their characteristic identification are defined in theheader section KO of the information packet, whereby the data to betransmitted are encoded in the data section or region with thecharacteristic identifications of the data symbol or symbols.Furthermore, the header section KO can be used for providing ortransferring characteristic values or parameters which, for example,control the evaluation of the data word. Furthermore, with the EOTsection or region, the receiver is informed of the end of theinformation packet by a prescribed characteristic identification.

Before a data exchange is carried out between a base station and one ormore transponders, identification codes of all transponders that arelocated in the field of the base station must be transferred to the basestation through an identification or selection of the transponders. Thismethod is also referred to as anti-collision and is preferably carriedout strictly hierarchically.

An identification code for a maximum of eight transponders isillustrated in the FIG. 1 b. In order to communicate to or activate oneof the eight transponders, a total of three bit planes or levels must berun through.

A selection of a first transponder in connection with a total of twotransponders is illustrated in the FIG. 2 a. After the transponders havenotified the base station of their presence in a reporting or log-onprocess, the duration of the reference interval RI is notified orreported by the base station in the header section in a followinginformation packet. Furthermore, in the header section, for the value ofthe data bit relative to the length of the reference interval RI, thetwo transponders are notified of the value {fraction (1/2)} for thelogical one and the value ¼ for the logical zero. In the data sectionfollowing the header section, in the first time interval Tx, bothtransponders notify or report the value of the first bit position oftheir identification code. At the end of the first time interval Tx,both transponders compare the length of the time interval with thelength of the reference interval RI.

1. Method for the selection of one or more transponders from a pluralityof transponders by a base station (BS) by means of an electromagneticwave, whereby an information packet (IP) is modulated onto theelectromagnetic wave, and the information packet (IP) comprises a headersection (KO) and a data section (DA), and the data section (DA) containsa data word with a sequence of bits, whereby one bit is allocated to thebit sequence respectively in a time interval (TX) generated from twosuccessive clock pulses, and an identification code embodied as a bitsequence is allocated to each transponder, and the transponders arewoken up by the base station by means of a log-on process, and as aresult of the log-on process, a pointer in the transponders points to afirst bit of the bit sequence of the identification code, characterizedin that in a first step, the time duration of a reference interval (RI)is transmitted in the header section (KO) of an information packet (IP)transmitted by the base station, in a second step, the time duration ofthe reference interval (RI) is stored in each transponder, in a thirdstep, at the beginning of the data section (DA) in a first time interval(TX) each transponder transmits the value of the first bit of theidentification code, in a fourth step, in each transponder at the end ofthe first time interval (TX) a comparison between time duration of thereference interval (RI) and the time duration of the first time interval(TX) is carried out, in a fifth step, a value is allocated to a test bitfrom the result of the comparison, in a sixth step, the transponderscompares the value of the test bit with the value of the first bittransmitted in the first time interval (TX), and the transponders, inwhich the value of the first bit of the bit sequence of theidentification code differs from the value of the test bit, are switchedinto a standby or silent mode until the beginning of a further log-onprocess, and the transponders, in which the value of the first bit ofthe bit sequence of the identification code corresponds with the valueof the test bit, transmit the value of the second bit of the bitsequence of their identification code in a second time interval (TX). 2.Method according to claim 1, characterized in that further transpondersor exactly one transponder are selected through a comparison of furtheror all bits of the bit sequence of the identification code, in that thesteps 4 to 6 are run-through multiple times, and after each run-throughthe number of the time interval (TX) and the number of the bit positionof the identification code is increased by one.